Process of coating article with laminate of metal and alumina

ABSTRACT

LAMINATES COMPRISING ALTERNATE LAYERS OF ELECTRODEPOSITED METAL OR ALLOY AND ALUMINA; SUCCESSIVE LAYERS MAY BE DEPOSITED FROM SEPARATE BATHS OR THE SAME BATH AND THE METAL MAY BE COPPER, WHICH MAY BE DEPOSITED FROM A SOLUTION CONTAINING COPPER CYANIDE OR COPPER PYROPHOSPHATE.

United States Patent rm. (:1. cisb 5/50, 11/00 US. Cl. 20442 9 Claims ABSTRACT OF THE DISCLOSURE Laminates comprising alternate layers of electrodeposited metal or alloy and alumina; successive layers may be deposited from separate baths or the same bath and the metal may be copper, which may be deposited from a solution containing copper cyanide or copper pyrophosphate.

This invention relates to laminates, and methods of producing same.

It is known that the tensile strength resistance to high temperatures of metal can be increased by forming a dispersion of a second phase of small particle size and distance between particles and various ways of producing such material have been suggested. We have found that alternate layers of metal or alloy and alumina can be deposited from solutions by alternate cathodic electrodeposition and anodic electrodeposition.

Accordingly, the present invention comprises a laminate comprising alternate layers of electrodeposited metal or alloy and alumina.

The invention further comprises a process for producing such a laminate by alternate cathodic electrodeposition of metal or alloy and anodic electrodeposition of alumina from alkaline solution.

The deposition of the alternate layers of alumina gives the lamination a hardness which is greater than that of plating with the metal or alloy alone. When alernate copper and alumina layers are employed, the hardness in at least some cases is twice or three times that of copper plating and does not exhibit a marked decrease at an annealing temperature of ZOO-300 C., as does non-laminated copper plating.

The laminate may form a laminated material or may be provided as a relatively thin coating on a substrate.

The laminate may be provided on any suitable material which may be normally coated by electrodeposition technique and especially, when the electrodeposited metal is copper, those metals which are often copper-plated in the art. Particularly good results are obtained when steel, brass, copper or aluminium are used as substrate.

A laminate formed of alternate layers of copper and alumina has the advantage that the copper offers good resistance to fouling, particularly by marine organisms, while the alumina provides good resistance to impingement attack arising from vortices and bubbles striking the laminate, and also cavitation and abrasion. Coatings formed of alternate layers of copper and alumina are therefore of particular value when applied, e.g., to condensor tubes and propellors.

3,556,958 Patented Jan. 19 1971 Other metals which may be electrodeposited include tin, zinc, iron, nickel, cobalt, chromium and alloys thereof.

The formation of the laminate is effected by alternate cathodic and anodic electrodeposition of the metal or alloy and alumina from appropriate alkaline solutions of salts. Thus, when copper is employed, cathodic deposition of the copper may be effected from solutions containing for example, copper cyanide or copper pyrophosphate, adjusted to an alkaline pH. Particularly good results are obtained using copper cyanide.

For anodic deposition of the alumina layers, suitable alkaline salt solutions include those containing sodium aluminate, adjusted to the required pH.

According to one embodiment of the invention, the laminate is formed by alternate electrodeposition in the copper-containing solution and then the aluminate-containing solution.

In a further embodiment of the invention, a mixed plating solution is used. In this case, the concentration of copper salts in the solution should be kept low owing to the very low efficiency of aluminium oxide deposition in the presence of higher concentrations of copper salts. Preferably the concentration of copper salts should not exceed 0.5% w/v. Alternate cathodic and anodic electrolysis is effected in the single solution to lead to alternate deposition of layers of copper and alumina.

The conditions for electrodeposition are selected as appropriate and will be well understood by those skilled in the art. In general, highly satisfactory results are obtained at a bath temperature of 50 C., allowing current flow for from 10 seconds up to 5 minutes per layer, using a current density of 40 amps/sq. foot for the cathodic plating phase and 20 amps/ sq. foot for the anodic plating phase.

The invention will further be understood by reference to the following examples:

EXAMPLE 1 A mild steel plate was immersed in an electro-plating bath containing a solution of following composition:

Gms./litre Cupric cyanide 30 Sodium cyanide 38 Sodium carbonate 39 The pH value of the solution was approximately 11 and a cathode current density of 40 amps/sq. foot at a temperature of 50 C. was applied to the steel plate. After depositing a layer of copper of approximately 0.0025" by treatment in the above conditions for about 5 mins. the steel plate was transferred to a bath containing:

Gms./litre Sodium aluminate 25 Tartaric acid 5 The pH value of the bath was approximately 11.2 and an anode current density of approximately 18 amps/sq. foot at a temperature of 50 C. was applied to the steel plate. Alumina was deposited for approximately seconds to give a layer approximately 0.0024" thick.

The work was then transferred back to the copper bath and the processes repeated until a laminate of 0.015" thickness formed by 600 layers has been built up.

It is found that a considerable quantity of the alumina deposit is redissolved on transfer to the copper bath so that the quantity of alumina found in successive layers is considerably less than the theoretical quantity, but considerable strengthening of the copper has taken place. Micro-hardness tests on copper deposited onto the steel plate from the same bath compared with that of the laminate gave the following results:

It was noted that the grain size of the laminate after annealing was considerably less than that of the pure copper. The oxide films consisted of fibres or plates of crystalline structure.

EXAMPLE 2 The experiment of Example 1 was repeated, on four further test plates, using the cathodic and anodic plating times as shown in the following table. The table also shows the VPN hardness following treatment of the plate at the indicated temperatures:

Cathodic Anodic plating plating Hardness VPN Test plate time time No. (secs) (secs) 20 0. 300 C. 600 C. 700 C.

EXAMPLE 3 By substituting copper, brass, and aluminium plates for the steel plate, and repeating the process of Example 1, similar results are obtained.

EXAMPLE 4 This example demonstrates the process of the invention using mixed solutions.

Three solutions, a b and c, of the following compositions were prepared:

Solution a, g./l b, g./l. c, g./1.

Steel test plates were electro-plated in each of the solutions; in each case, cathodic plating was alternated with anodic plating for the times shown in the table below. The cathodic current density was 40 amps/ sq. foot and the anodic current density was 20 amps/sq. foot. The bath temperature was 50 C. A laminate of 0.015" thickness formed by 600 layers was built up.

Following treatment, the plated surface coating was examined for VPN hardness, after temperature treatment as indicated:

Cathodic Anodie plating plating Hardness VPN time time Solution (secs) (secs) 20 0. 300 0. 600 C. 700 C.

Substitution of copper, brass and aluminium plates for the steel plates of this experiment leads to similar resul s.

4 EXAMPLE 5 This example demonstrates a process according to the invention for forming a laminate of alternate layers of zinc and alumina using a mixed solution.

A solution of the following composition was prepared:

Steel test plates were electro-plated in the solution, cathodic plating alternating with anodic plating. The cathodic current density was 40 amps/ sq. foot and the anodic current density was 20 amps/ sq. foot, the bath temperature being 50 C., and the pH value of the bath being 11. A laminate of 0.015" thickness formed by 600 layers was built up.

After the treatment, the plated surface coating was examined for VPN hardness, after temperature treatment, and it was found that at temperatures up to 200 C., at which the VPN hardness of a test plain zinc coating was about 60, the VPN hardness of the laminate was considerably higher, and in one case as high as 320, the hardness of the laminate decreasing as the temperature increased. Considerable variations in the hardness of the laminate were found when the process was repeated, and these variations were believed to result from exhaustion of one or more of the bath components, particularly the sodium aluminate.

We claim:

1. A process for coating an article with a laminate comprising a plurality of alternating layers of metal or alloy with alumina which comprises the steps of cathodically electrodepositing a metal or alloy on said article, anodically electrodepositing alumina from an aqueous alkaline solution, followed by alternately repeating said anodic and said cathodic electrodeposition until the desired number of alternating layers is achieved.

2. A process according to claim 1, wherein the electrodeposition is effected by alternate cathodic electrodeposition and anodic electrodeposition in a common solution which contains both copper salts and an aluminate.

3. A process according to claim 2, wherein the concentration of copper salts in the common solution does not exceed 0.5% w./v.

4. A process according to claim 1, wherein the metal is copper and is electrodeposited from a solution containing copper cyanide.

5. A process according to claim 1, wherein the metal is copper and is electrodeposited from a solution containing copper pyrophosphate.

6. A process according to claim 1, wherein the alumina is electrodeposited from a solution containing sodium aluminate.

7. A process according to claim 1, wherein the electrodeposition is effected by alternate cathodic electrodeposition in a solution containing copper salts and anodic electrodeposition in a solution containing an aluminate.

8. A process for coating a substrate selected from the group consisting of steel, brass, copper or aluminum with a laminate comprising a plurality of alternating layers of metal or alloy selected from the group consisting of copper, tin, zinc, iron, nickel, cobalt, chromium and alloys thereof and a plurality of electrodeposited layers of alumina comprising the steps of cathodically electrodepositing said metal or alloy on said substrate, anodically electrodepositing said alumina from an aqueous alkaline solution, followed by alternate anodic and cathodic electrodeposition until the desired number of layers is achieved.

9. A process according to claim 8 wherein the current density of said cathodic electrodeposition is about 40 amps/ sq. ft. and the current density of said anodic electro- UNITED deposition is about 20 amps/sq. ft., said alkaline solution having a pH of about 11 and the current in both said anodic and cathodic electrodeposition being maintained for about 10 seconds to about 5 minutes per layer.

References Cited STATES PATENTS Truesdale et al 204-56 Sumner et a1 20456X Wheildon, Jr 29195X Aves, Jr., et a1. 29-195X Aves, Ir. 29-195X OTHER REFERENCES A. G. Gray: Modern Electroplating, pp. 198 and 10 GERALD L. KAPLAN, Primary Examiner US. Cl. X.R. 

